Embodiments of the subject matter disclosed herein generally relate to actuated valves used in reciprocating compressors for oil and gas industry, and, more particularly, to mechanisms and techniques related to valves in which valve closing members are attached to actuated counter-seats.
Compressors are mechanical devices used to increase the pressure of a gas and can be found in engines, turbines, power generation, cryogenic applications, oil and gas processing, etc. Due to their widespread use, various mechanisms and techniques related to compressors are often subject to research for improving the compressor efficiency and solving problems related to specific situations. One particularity that has to be considered for compressors used in oil and gas industry is that the compressed fluid is frequently corrosive and inflammable. American Petroleum Institute (API), the organization setting the recognized industry standard for equipment used in oil and gas industry has issued a document, API618, listing a complete set of minimum requirements for reciprocating compressors.
The compressors may be classified as positive displacement compressors (e.g., reciprocating, screw, or vane compressors) or dynamic compressors (e.g., centrifugal or axial compressors). For positive displacement compressors, the compression is achieved by trapping the gas and then reducing volume in which the gas is trapped. For dynamic compressors, the gas is compressed by transferring kinetic energy, typically from a rotating element such as an impellor, to the gas being compressed by the compressor.
FIG. 1 is an illustration of a conventional dual chamber reciprocal compressor 10 useable in oil and gas industry. Compression occurs in a cylinder 20. A fluid to be compressed (e.g., natural gas) is input into the cylinder 20 via an inlet 30, and, after being compressed, it is output via an outlet 40. The compression is a cyclical process in which the gas is compressed by movement of the piston 50 along the cylinder 20, between a head end 26 and a crank end 28 of the cylinder 20. In fact, the piston 50 divides the cylinder 20 in two compression chambers 22 and 24 operating in different phases of the compression cycle, the volume of compression chamber 22 being at its lowest value when the volume of the compression chamber 24 is at its highest value and vice-versa.
Suction valves 32 and 34 open to allow the fluid that is going to be compressed (i.e., having a first pressure p1) from the inlet 30 and through the suctions valves 32 and 34 into the compression chambers 22 and 24, respectively. Discharge valves 42 and 44 open to allow the fluid that has been compressed (i.e., having a second pressure p2) to be output from the compression chambers 22 and 24, respectively, via the outlet 40. The piston 50 moves due to energy transmitted from a crankshaft 60 via a crosshead 70 and a piston rod 80.
Conventionally, the suction and the compression valves used in a reciprocating compressor are automatic valves that are switched between close and open due to a differential pressure across the valve. FIGS. 2A and 2B illustrate the operation of an automatic valve 100 having a seat 110 and a counter-seat 120. A distance d between the seat 110 and the counter-seat 120 is constant throughout the compression cycle (for example, a spacer 115 may be located there-between). FIG. 2A illustrates the valve 100 in an open state and FIG. 2B illustrates the valve 100 in a close state.
In the open state illustrated in FIG. 2A, the valve closing member 130 is pushed down into the counter-seat 120 allowing the fluid to flow through a inlet port 140 and outlet ports 150. The shape of the valve closing member 130 may be a disc, a poppet, multi-poppet or rings, which difference in shape gives the name of the valve: disc valve, poppet valve, multi-poppet valve or ring valve. FIGS. 2A and 2B represent a generic configuration independent of the details related to the actual shape of the valve closing member 130. FIG. 3 illustrates components of a ring valve which operate as in FIGS. 2A and 2B: the seat 110 and the counter-seat 120 having circular openings of the ports 140 and 150 on their surfaces, springs 160 on the counter-seat 120 and rings 131 (which are the valve closing member).
In FIG. 2A, a spring 160 is located between the valve closing member 130 and the counter-seat 120. Depending on its state of deformation, the spring 160 actively participates in establishing a valve opening point, the elastic deformation force superimposing a pressure along the flow path equal to the force divided by the area of the valve closing member 130. In the open state, the first pressure p1 before the inlet port 140 is larger than the pressure p2 at the destination of the fluid after the outlet ports 150. If the spring 160 is deformed when the valve closing member 130 is pushed down into the counter-seat 120 (as shown in FIG. 2A), the difference (p1−p2) between the pressures before and after the valve has to be larger than the pressure due to the spring 160 (i.e., a ratio of the elastic deformation force divided by the area of the valve closing member).
In the close state illustrated in FIG. 2B, the valve closing member 130 prevents the fluid flowing from the inlet port 140 towards the outlet ports 150. The spring 160 is often configured to favor a faster closing of the valve, and, therefore, it is known as a “return” spring closing the valve 100 even if the pressures at the source p1 and the destination p2 are equal (p1=p2).
As described above, the valves in a reciprocating compressor may be switched between the open state and the close state due to the pressure difference between the pressure p1 at the source of the fluid and the pressure p2 at the destination of the fluid. The springs are used to accelerate the switching between the open and close states, while the pressure difference across the valve (p1−p2) may change dynamically. Alternatively, the valve closing member may be actuated by an electromagnetic or hydraulic actuator applying a force to move the valve closing member.
The spring is a part of the valves that frequently fails, affecting reliability of the valve, and, thus, of the whole reciprocating compressor. Additionally, in time, fluttering may occur, that is asymmetries due to the springs may disrupt the motion of the valve closing member allowing leakage. When actuators are used, the force due to the spring may have to be overcome by the actuator force in some situations occurring during the valve operation.
Further, one inefficiency to the reciprocating compressor is related to the clearance volume, that is, a volume from which the compressed fluid cannot be evacuated. Part of the clearance volume is due to volume related to the valves. A design objective is to make this clearance volume as small as possible.
Accordingly, it would be desirable to provide valves without springs that avoid the afore-described problems and drawbacks.